Appending Java serialized objects

Question

I need a little bit of help in Java File IO operations. I am trying to append the serialized object to my file but only the last Object is being appended to the file. I have tried many suggestions but no success yet. How I can achieve this, please help?

Here is my Code:

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Scanner;




public class Working {

     String FILENAME = "E:\\assignment\\userpass\\userpass.txt";

    Scanner sc = new Scanner(System.in);
    String sUser = null, sPass = null, sRole = null;

    Signup signup = new Signup();

    public void createUser(){

        System.out.println(" Enter username: ");
        sUser = sc.next();

        System.out.println(" Enter password: ");
        sPass = sc.next();

        System.out.println(" Enter Role: ");
        sRole = sc.next();


        Working obj = new Working();

        signup.setUsername(sUser);
        signup.setPassword(sPass);
        signup.setRole(sRole);

        obj.serializeUser(signup);


    }





public void serializeUser(Signup signup){

        FileOutputStream fout = null;
        ObjectOutputStream oout= null;

        File file = new File(FILENAME);

        try{

        //  fout = new FileOutputStream(file);
        //  fout = new FileOutputStream(file.getAbsoluteFile(), true);
            fout = new FileOutputStream(file, true);
        //  fout = new FileOutputStream(FILENAME);
            oout = new ObjectOutputStream(fout);
            oout.writeObject(signup);

            System.out.println("User has been serialized");

        } catch(Exception e){
            e.printStackTrace();

        } finally {

            if(fout != null){
                try{

                    fout.close();
                } catch(IOException e){
                    e.printStackTrace();
                }
            } 

            if(oout != null){
                try{

                    oout.close();
                } catch(IOException e){
                    e.printStackTrace();
                }
            } 

        }

    }


// for test purpose
public void showUsers(){
    Working obj = new Working();
    Signup add = obj.deserializeUser(FILENAME);

    System.out.println(add);
}

// to show data
//test purpose

public Signup deserializeUser(String filename){

    Signup userDetails = null;
    File file = new File(FILENAME);

    FileInputStream fin = null;
    ObjectInputStream oin = null;

    try{

        fin = new FileInputStream(file);
        oin = new ObjectInputStream(fin);

        userDetails = (Signup) oin.readObject();

    } catch(Exception ex){
        ex.printStackTrace();
    } finally{
        if (fin != null) {
            try {
                fin.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (oin != null) {
            try {
                oin.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return userDetails;

}

}

I have checked here already: 1. http://www.enseignement.polytechnique.fr/informatique/Java/1.8/java/io/FileOutputStream.html#FileOutputStream-java.lang.String-boolean- 2. Appending to an ObjectOutputStream

A quick glance at the ObjectOutputStream document doesn't lead me to believe there is an overload to writeObject that will append new objects. I think there's good reason for that. You may want to consider not serializing the object directly, but serialize it to string, and then write that to a file using the an outputstream with an append option. Deserialization would involve unmarshalling each line in your file to a new Signup object. Alternatively you could serialize a collection of your objects, and unmarshall the same collection type from it. — Mark W, Aug 29 '17 at 19:07
@EJP I was suggesting he serialize it to a string. There is no reason why he couldn't marshall his object to a string. The string can be anything from XML to comma delimited key value pairs for the fields. Doesn't really matter. Serialization is serialization, regardless of the storage format. — Mark W, Aug 29 '17 at 19:59
@MarkW He is using Java Object Serialization. It produces a binary format. You can't serialize that to a `String`. If you're recommending he use a different serializer you needed to say so. — user207421, Aug 29 '17 at 20:06
@EJP, I misread that first time around.... nevertheless. I said serialize, not binary serialize with an object serializer. Serialization is not exclusively using this particular serialization method. My comment seems perfectly clear to me. — Mark W, Aug 29 '17 at 20:12
@MarkW It isn't 'clear' in a question about Java Object Serialization, it's wrong. Without the information that you're talking about a different form of serialization (and incidentally one that doesn't use a binary format, not stated), the OP would be misled into trying it with his existing code and run into the problem that ... `String` isn't a container for binary data. This seems perfectly clear to me. — user207421, Aug 30 '17 at 00:47

user207421 · Answer 1 · 2017-08-29T19:49:57.757

You need to create a new Signup object every time around the loop, or else call ObjectOutputStream.reset() each time, or use ObjectOutputStream.writeUnshared().

However there are other problems.

You should close the object output stream before the file output stream, or instead of.
You can't append to an object output stream, at least not as simply as this. See my answer about 'StreamCorruptedException - invalid type code AC' for why not. You need to use the technique in your second link.

Appending Java serialized objects

1 Answers1